1. Field of the Invention
The present invention relates to a non-aqueous ink that is suitable for use with an inkjet recording system, and more particularly to a non-aqueous ink that provides an excellent effect of reducing or eliminating print-through (striking-through), thereby achieving high print density.
2. Description of the Related Art
An inkjet recording system ejects a highly fluid inkjet ink as an ink particle from a very thin head nozzle to record an image on printing paper, which is positioned to face the nozzle. Because of low noise and ability of high-speed printing, the inkjet recording systems are rapidly becoming widely used in recent years. As inks for use with the inkjet recording systems, various types of so-called non-aqueous pigment inks, which are formed by finely dispersing a pigment in a non-water-soluble solvent, are proposed.
For example, the applicant of the present application has proposed, in Japanese Unexamined Patent Publication No. 2007-126564 (hereinafter, Patent Document 1), a non-aqueous ink including a pigment and an organic solvent, which includes an ester solvent, a higher alcohol solvent, a hydrocarbon solvent, etc., and further including a soluble polymeric dispersant. This ink is advantageous in that it has excellent on-machine stability and is suitable for inkjet, and it can provide a printed surface that does not adhere to another printed surface printed with a PPC duplicator or a laser printer even when they are stacked in contact with each other, and thus is highly suitable for toner. Further, Japanese Unexamined Patent Publication No. 2007-197500 (hereinafter, Patent Document 2) discloses a non-aqueous ink including a pigment and an organic solvent, which includes an ester solvent and/or a hydrocarbon solvent, and further including a dispersible polymeric dispersant (NAD).
Conventional pigment-dispersed non-aqueous inks ensure dispersion stability of the pigment by using a resin or polymeric dispersant (soluble dispersant or NAD), as taught in Patent Document 1 or 2, or by directly modifying the surface of the pigment with a polymer (such as by grafting or microencapsulation). These approaches are to physically reduce or eliminate agglomeration of the pigment by providing steric hindrance by the polymer. In other words, these approaches attempt to improve the dispersion stability of the pigment in the ink by adding the polymer component in the ink.